1. Field of the Invention
The present invention relates to a welded structure for a boss and a bracket to be mounted in a cylindrical structure made of a sheet metal, and a welding method therefor.
2. Related Art
FIG. 9 is a sectional view showing one example of a cylindrical body having a boss in its inside and made of a sheet metal. In a cylindrical body 50 having a rectangular section and constructed of vertically opposed upper and lower sheets 51 and 51 and horizontally opposed side sheets 52 and 52, there are arranged a boss for a mounting pin having a seat 54, and a boss 55 having a seat 56. These seats 54 and 56 are individually deposited on the right and left side sheets 52 and 52 from the inner side of the cylindrical body 50. In the bosses 53 and 55, there are formed pin mounting holes 57 which extend therethrough in the axial directions. Holes are also formed coaxially with the holes 57 and 57 through the side sheets 52 and 52. In this structure, for example, the cylinder rod head 61 of a hydraulic cylinder to be mounted in the cylindrical body 50 is mounted by sandwiching it between the bosses 53 and 55 and by inserting amounting pin 60, as indicated by double-dotted lines in FIG. 9, into the holes 57 and 57 and the mounting hole of the rod head 61.
The cylindrical body 50 is manufactured by depositing the boss 53 and the seat 54, the boss 55 and the seat 56 at first, then the seats 54 and 56 on the right and left side plates 52 and 52, and then the side plates 52 and 52 and the upper and lower sheets 51 and 51, to construct the rectangular cylindrical body 50.
When the welded structure having the construction described above is manufactured, however, the bosses 53 and 55 and the seats 54 and 56 are deposited in advance on the side sheets 52 and 52, and then the side sheets 52 and 52 and the upper and lower sheets 51 and 51 are deposited at the four corners to construct the rectangular cylindrical body 50. This construction raises a problem that the manufacture has many steps and a long welding line and takes a long time and a high cost. Another problem is that the cylindrical body 50 has an increased total weight. Moreover, the numerous sheets are deposited to construct the cylindrical body so that the deposited portions have to be strengthened for enhancing the rigidity of the structure, but this high rigidity is hard to attain.
In recent years, with a view to solving these problems, it has been proposed for the arm of a working implement of a construction machine to form a compact cylindrical body by bending a sheet metal so as to raise the rigidity, to lessen the weight, to improve the field of view and to lower the cost. In this case, various shapes including circular and triangular shapes can be conceived as the sectional shape, which is exemplified by one of a generally triangular cylindrical body 71, as shown in FIG. 10. This cylindrical body 71 is manufactured by a process including the steps of: bending a sheet material 70 upward at first in the vicinity of its two end portions, as indicated by double-dotted lines; next bending the right and left portions upward, as indicated by arrows, on the apex of the triangle into the shape shown by solid lines; and finally depositing the central portion P of the base of the triangle, as located at an upper portion.
In the manufacture case having the aforementioned steps, when the bosses 53 and 55 or the bracket for the mounting pins is deposited in the prepared cylindrical body 71, the outer peripheral portions of the bosses 53 and 55 and the bracket have to be deposited, according to the process of the prior art, on the cylindrical body 71 from the inner side of the cylindrical body 71. In the manual welding case, therefore, the worker is required to perform the welding work by inserting the welding torch into the small-sized cylindrical body 71 while substantially failing to observe the welding line, so that sufficient welding strength and precision cannot be retained. Even with an automatic welding apparatus such as a welding robot, alternatively, it is extremely difficult to move the robot arm or the welding torch in the narrow space of the cylindrical body and to automate the welding work. On the other hand, it is also conceivable to form the cylindrical body 71, after the boss 53 for the mounting pin and the bracket were deposited in advance on a sheet metal, by bending the sheet metal. According to this method, however, there is a problem that the sheet metal cannot be precisely bent because it is blocked by the deposited boss or the like. This problem makes it seriously difficult to practice that method.
From the discussion thus far made, it is an important target to achieve a welding method capable of depositing the boss or the bracket highly precisely and firmly in the cylindrical body formed in advance of the sheet metal.
Noting the problems thus far described, therefore, the present invention has an object to provide not only such a welded structure for a boss and a bracket in a cylindrical body as can have a light weight, retain a rigidity, an excellent durability and an easy manufacture but also a welding method therefor.
In order to achieve the above-specified object, according to a first invention, in a sheet metal structure including at least one of a boss and a bracket for mounting a member is mounted in a cylindrical body, a welded structure for a boss and a bracket is constructed: by boring holes of predetermined shapes in predetermined portions on the side face of a cylindrical body made of a sheet metal; by inserting seats of at least one of a boss and a bracket from the inner side into said holes; by mounting the member mounting portions of said boss and said bracket in said cylindrical body; and by welding the individual seats of said boss and said bracket on the side face of said cylindrical body from the outer side of said cylindrical body.
According to the first invention, the bores are formed in the side face of the prepared cylindrical body of the sheet metal, and the boss or the bracket and the side face of the cylindrical body are deposited from the outer sides of the holes. Even where the cylindrical body is made compact to fail to retain a space therein for the welding torch or the like to move, the boss or the bracket can be easily and reliably mounted and welded in the cylindrical body. This makes it possible to increase the degree of freedom for designing the sectional shape of the cylindrical body, to provide a light and highly rigid cylindrical body easily, to simplify the structure and to lower the cost.
According to a second invention, there is provided a welding process for a boss and a bracket of a sheet metal structure including at least one of a boss and a bracket for mounting a member is mounted in. a cylindrical body. The welding process comprises:
a) forming a cylindrical body of a thin sheet metal;
b) boring holes of predetermined shapes in predetermined portions on the side face of said cylindrical body;
c) inserting seats of at least one of a boss and a bracket from the inner side into said holes, and mounting the member mounting portions of said boss and said bracket in said cylindrical body; and
d) welding the individual seats of said boss and said bracket on the side face of said cylindrical body from the outer side of said cylindrical body.
According to the second invention, the pin mounting portion for the boss or the bracket, as prepared separately in advance, can be mounted in the cylindrical body prepared in advance, and the boss or the bracket can be deposited easily, highly accurately and reliably on the side face of the cylindrical body thereby to improve the welding workability of the boss or the bracket.
According to a third invention, in a working implement for a construction machine including at least one of a boss and a bracket for mounting a drive unit of an arm outside of a cylindrical body and for mounting a drive unit of a working attachment inside of said cylindrical body, a welded structure for a boss and a bracket is constructed: by boring holes of predetermined shapes for releasing the concentration of stress, in predetermined portions on the side face of a cylindrical body made of a sheet metal; by providing at least one of a boss and a bracket for mounting a drive unit of a working attachment, with seats shaped so substantially similar to said holes as to cover said holes; by inserting said seats from the inner side into said holes; by mounting the attaching portion of the drive unit of the working attachment of said boss and said bracket for mounting the drive unit of the working attachment, in said cylindrical body, and covering said holes with said seats; and by welding said seats on the side face of said cylindrical body from the outer side of said cylindrical body.
According to the third invention, the boss or the bracket for mounting the drive unit of the working attachment can be arranged in the cylindrical body of the sheet metal and deposited on the side face of the cylindrical body thereby to increase the degree of freedom for designing the sectional shape of the cylindrical body, to simplify the structure, to lessen the weight, to improve the field of view and to lower the cost. On the other hand, the holes of the deposited portions on the side face of the cylindrical body and the seats for the boss and the bracket are shaped to release the stress concentration, thereby to make it possible to reduce the stress to occur at the deposited portion, to reduce the fear of the breakage of the deposited portion and to improve the durability of the case in which the cylindrical body is applied to the arm of the working implement of the construction machine.
According to a fourth invention, there is provided a welding process for a boss and a bracket of a working implement for a construction machine including at least one of a boss and a bracket for mounting a drive unit of an arm outside of a cylindrical body and for mounting a drive unit of a working attachment inside of said cylindrical body. The welding process comprises:
a) forming a cylindrical body of a thin sheet metal;
b) welding at least one of the boss and the bracket for mounting the drive unit of the arm, on the outer portion of said cylindrical body;
c) boring holes of predetermined shapes for releasing the concentration of stress, in predetermined portions on the side face of said cylindrical body;
d) providing at least one of a boss and a bracket for mounting the drive unit of the working attachment, with seats shaped so substantially similar to said holes as to cover said holes;
e) inserting said seats from the inner side into said holes, mounting the attaching portion of the drive unit of the working attachment of said boss and said bracket for mounting the drive unit of the working attachment, in said cylindrical body, and covering said holes with said seats; and
f) welding said seats on the side face of said cylindrical body from the outer side of said cylindrical body.
According to the fourth invention, there is arranged in the cylindrical body prepared of the sheet metal the pin mounting portion of the boss or the bracket for mounting the drive unit of the working attachment, as prepared separately in advance, so that the seat of the boss or the bracket can be deposited highly precisely and firmly on the side face of the cylindrical body. It is, therefore, unnecessary to deposit the boss or the like in advance in the cylindrical body, and especially the bracket can be deposited, after bored in advance with the pin hole, in the cylindrical body. Therefore, the manufacture process for manufacturing the arm of the working implement from the cylindrical body can be simplified to make it possible to facilitate the welding work, to shorten the manufacture time and improve the working efficiency, and to lower the cost. Moreover, the side face of the cylindrical body is bored with the holes having the smooth shape to release the stress concentration, and the shape of the seat is made generally similar to that of the hole thereby to make it hard to cause the stress concentration at a welded portion between the hole and the seat when a load is applied, and possible to improve the durability.
According to a fifth invention, as based on the method of the second or fourth invention, there is provided a welding process which further comprises: working, after the individual seats of said boss and said bracket mounted in said cylindrical body were deposited from the outer side of said cylindrical body, said deposited portions generally flush with the outer side face of said cylindrical body.
According to the fifth invention, no weld bead protrudes from the outer surface of the cylindrical body so that the stress concentration can be reduced at the welded portion. At the same time, the outer surface of the cylindrical body provides a smoothly slidable face so that the present cylindrical body can be applied to the inner arm of the multistage extendible arm.